1. Field of the Invention
The present invention is directed to LCD, LCOS, D-ILA or digital micromirror device (DMD) projectors incorporating light engines with color splitting-converging prisms, and more particularly to a projector with a light valve that is sealed against the glass prism surface by a dust-free air channel.
2. Description of the Related Art
In a typical color projector, a light valve is imaged onto a screen by a projection lens to produce an image. Dust that circulates through the projector by the air cooling system can settle on the light valve and also be imaged onto the image screen. The dust causes color blemishes and can reduce contrast in projectors capable of greater than 1500:1 contrast ratio.
A variety of techniques have been proposed for sealing dust out of a projector. U.S. Pat. No. 6,280,036 describes a method of mechanically sealing the light valve to a field lens in order to eliminate dust. U.S. Pat. No. 6,394,608 and US Patent Application 2002/0033992 A1 describe sealing the light valve and optical system inside a dust-proof box. A similar technique is proposed in U.S. Pat. No. 6,350,033. All of the foregoing prior art techniques are suitable for low-lumens applications (3000 lumens) and/or single chip projectors. In the case of three-chip projectors, the rated lumens can be from 6000 up to 20000 lumens. With such high-lumens output, air should be circulated around the light valves in order to maintain the manufacturer's temperature ratings. Also, three-chip projectors often have convergence adjustment on each of the red, green, and blue channels. Sealing the light valves in a dust sealed chamber therefore prevents convergence adjustment. Although it is common to dust seal the projector using various types of air filters, over time dust will enter the projector and eventually settle on the light valve surface.
Accordingly, it is an objective of the present invention to provide cooling and dust sealing to display devices mounted on a prism without limiting access for convergence adjustment on the display devices and maintaining display device temperatures within manufacturer's ratings.